Sensor interface system

ABSTRACT

A sensor interface system for providing a connection between at least one sensor and a maternal-fetal monitor, wherein the interface system converts electrical muscle activity captured by the sensor(s) into uterine activity data signals for use by the maternal-fetal monitor. The sensor interface system of the invention preferably includes a conversion means for converting the signals from the sensor(s) into signals similar to those produced by a tocodynamometer.

CROSS-REFERENCE TO A RELATED APPLICATION

This application is a Continuation of U.S. application Ser. No.13/292,787, filed Nov. 9, 2011, which claims the benefit of U.S.Provisional Application No. 61/411,702, filed Nov. 9, 2010, and is aContinuation-in-Part of U.S. application Ser. No. 12/941,614, filed Nov.8, 2010, now U.S. Pat. No. 9,307,919, which is a continuation of U.S.patent application Ser. No. 11/582,714 filed Oct. 18, 2006, now U.S.Pat. No. 7,828,753, all of which are incorporated herein by reference intheir entirety.

BACKGROUND OF INVENTION

Assessment of the fetus during pregnancy, and particularly during laborand delivery, is an essential yet elusive goal. While most patients willdeliver a healthy child with or without monitoring, more than 5 out ofevery 1,000 deliveries of a viable fetus near term are stillborn, withhalf having an undetermined cause of death. (National Vital StatisticsSystem (NVSS), CDC, NCHS as published in “Healthy People 2010,Understanding and Improving Health: Chapter 16,” co-authored by theCenters for Disease Control and Prevention and Health Resources andServices Administration, 2^(nd) Edition, U.S. Government PrintingOffice, November 2000). The risk of this unfortunate consequence isincreased in a subgroup of “high risk” patients (e.g., diabetics). Inaddition to regular obstetric observation, after 23 weeks gestationantepartum (“in utero”) fetal monitoring consists of the following (inorder of complexity):

-   -   1. maternal report of fetal movement;    -   2. non-stress test (NST)—monitor fetal heart rate (FHR) by        ultrasound, looking for baseline rate, variability and presence        of accelerations above the baseline;    -   3. contraction stress test (CST)—response of the FHR to uterine        contractions, either natural or induced; and    -   4. biophysical profile (BPP)—NST plus ultrasonographic        evaluation of fetal movements and amniotic fluid volume.

Despite their wide acceptance, these tests offer limited predictivevalue, and give only a glimpse of the fetus at the time of testing. Forhigh risk patients, once or twice weekly surveillance is oftenindicated, entailing both expense and inconvenience for the patient.

Intrapartum fetal surveillance is accomplished routinely withintermittent auscultation or continuous Doppler monitoring of the FHR,together with palpation or tocodynamometry (strain gauge) monitoring ofcontractions. When indicated, more invasive monitors are available, butrequire ruptured membranes/adequate cervical dilation, and entail somerisk, primarily infectious. These monitors include, without limitation:

-   -   1. fetal scalp electrode—a wire electrode inserted into the        fetal scalp;    -   2. intra-uterine pressure catheter (IUPC)—enables quantitative        measurement of contractions; and    -   3. fetal scalp sampling—a blood sample drawn for pH analysis.

Contraction detection allows monitoring of the progress of labor. Adevice commonly used in monitoring contractions is the tocodynamometer.The tocodynamometer detects physical changes in the curvature of themother's abdomen (usually with a strap or belt that is placed about theabdomen) during a contraction and translates these changes into aprinted curve. The tocodynamometer detects only the presence or absenceof tension on the abdomen (whether from uterine contraction or maternalmovement), and often fails in the presence of obesity. Unfortunately,patients are recommended to remain in a supine position when using atocodynamometer to monitor labor, which has been found to be the leasteffective physiological position for encouraging fetal internal rotationand often causes maternal hypotension and discomfort.

When cervical dilation lags behind the anticipated labor curve, oxytocinis often indicated to induce a more effective contraction pattern. Safetitration of the oxytocin may require accurate determination of“montevideo units” which measure the strength of uterine contractionsover 10 minutes. This requires the more invasive IUPC, a catheter placedinto the uterus, alongside the fetus, to measure the pressure generatedby uterine contractions.

The rationale for use of intrapartum electronic fetal monitoring (EFM)assumes that FHR abnormalities accurately reflect hypoxia (inadequateoxygen to the fetus), and that early recognition of this could induceintervention to improve outcome for both mother and fetus.Unfortunately, numerous studies have failed to identify this improvedoutcome with the use of EFM in low-risk deliveries. In fact some studieshave actually shown an increase in morbidity from a higher operativedelivery rate. Perhaps this should not be surprising in light of thevariability in interpretation of FHR tracings and their lack ofspecificity for hypoxia. Yet, continuous EFM remains the standard ofcare in US hospitals, in large part due to medical and legal concerns.

Recently, analysis of the fetal ECG (electrocardiogram) has heldpromise, with some features of the waveform more specifically indicatingfetal hypoxia. Use of the waveform analysis reduced the incidence ofsevere metabolic acidosis at birth, while necessitating fewer scalpsamples and operative deliveries. Unfortunately, acquisition of the FECGwas through the fetal scalp electrode described above which is bothinvasive and limited in its application. The necessity for access to thefetal scalp requires both adequate cervical dilation and rupturedmembranes, eliminating this procedure for antepartum fetal surveillance,as well as early labor.

Non-invasive acquisition of the FECG is a recognized issue of mixedsignals. Electrodes placed on the skin surface will record alltransmitted electrical activity including maternal ECG, maternalskeletal muscle, uterine muscle, fetal skeletal muscle, and fetal ECG.To address the inadequacies noted above, various methods have beenproposed for use in processing maternal abdominal signals to providemore accurate FECG extraction. These methods include subtractivefiltering (see, for example, U.S. Pat. No. 4,945,917), adaptivefiltering (see, for example, Widrow, B. et al., “Adaptive NoiseCanceling: Principals and Applications,” Proc. IEEE, 63(12):1692-1716(December 1975); Adam, D. and D. Shavit, “Complete Fetal ECG MorphologyRecording by Synchronized Adaptive Filtration,” Med. & Biol. Eng. &Comput., 28:287-292 (July 1990); Ferrara, E. and B. Widrow, “FetalElectrocardiogram Enhancement by Time Sequenced Adaptive Filtering,”IEEE Trans. Biomed. Eng., BME-29(6):458-460 (June 1982); U.S. Pat. Nos.4,781,200 and 5,042,499), orthogonal basis (Longini, R. et al., “NearOrthogonal Basis Function: A Real Time Fetal ECG Technique,” IEEE Trans.On Biomedical Eng., BME-24(1):39-43 (January 1977); U.S. Pat. No.5,042,499), linear combination (Bergveld, P. et al., “Real Time FetalECG Recording,” IEEE Trans. On Beiomedical Eng., BME-33(5):505-509 (May1986)), single value decomposition (Callaerts, D. et al., “Comparison ofSVD Methods to Extract the Fetal Electrocardiogram from CutaneousElectrodes Signals,” Med. & Biol. Eng. & Comput., 28:217-224 (May 1990);U.S. Pat. No. 5,209,237), and MECG averaging and correlation (Abboud, S.et al., “Quantification of the Fetal Electrocardiogram Using AveragingTechnique,” Comput. Biol. Med., 20:147-155 (February 1990); Cerutti, S.et al., “Variability Analysis of Fetal Heart Rate Signals as Obtainedfrom Abdominal Electrocardiographic Recordings,” J. Perinat. Med.,14:445-452 (1986); J. Nagel, “Progresses in Fetal Monitoring by ImprovedData Acquisition,” IEEE Eng. Med. & Biol. Mag., 9-13 (September 1984);Oostendorp, T. et al., “The Potential Distribution Generated by FetalHeart at the Maternal Abdomen,” J. Perinat. Med., 14:435-444 (1986);U.S. Pat. No. 5,490,515). These methods, unfortunately, do not reliablyenable continuous extraction of maternal-fetal data or cannot capture acomprehensive account of maternal-fetal health based on a combination oftest results (i.e., fetal heart rate, fetal ECG, maternal ECG, andmaternal uterine activity (EHG)).

Recently, magnetocardiography has been utilized in extracting fetal ECG(see, for example, Sturm, R. et al., “Multi-channel magnetocardiographyfor detecting beat morphology variations in fetal arrhythmias,” PrenatDiagn, 24(1):1-9 (January 2004); and Stinstra, J. et al, “Multicentrestudy of fetal cardiac time intervals using magnetocardiography,” BJOG,109(11): 1235-43 (November 2002)). Unfortunately, magnetocardiography islimited in application, technologically complex, and difficult toadminister to assess accurate fetal ECG readings.

Uterine contractions are the result of the coordinated actions ofindividual myometrial cells. At the cellular level, the contractions aretriggered by a voltage signal called an action potential. Duringpregnancy, cellular electrical connectivity increases such that theaction potential propagates to produce a coordinated contractioninvolving the entire uterus. The action potential during a uterinecontraction can be measured with electrodes placed on the maternalabdomen resulting in a uterine EMG signal (hereinafter referred to as“EHG”: electrohysterogram). Specifically, the EHG signal can beprocessed to produce a signal that is similar to the standard uterineactivity signal from the tocodynamometer or IUPC. The EHG providescontraction frequency and duration information. To date, EHG signalshave not been used in assessing the intra-uterine pressure or predictingmontevideo units.

Postpartum, continuous uterine contraction is required to minimizeuterine bleeding from the placental detachment site. Hemorrhage is theleading cause of peripartum maternal death, and most of these arepostpartum hemorrhage due to this “uterine atony.” Current monitoringconsists of serial uterine palpation at intervals of several hours.Diagnosis is usually made by patient complaint of severe bleeding, orhypovolemic shock (from hemorrhage). Neither IUPC nor tocodynamometermonitoring is available at this time. The EHG would provide a uniquemeans for monitoring the uterine tone, providing an early warning ofatony and potential hemorrhage.

Devices that utilize invasive techniques for monitoring fetal healthinclude those disclosed in U.S. Pat. Nos. 6,594,515; 6,115,624;6,058,321; 5,746,212; 5,184,619; 4,951,680; and 4,437,467.

Accordingly, a cost-effective, more reliable system and method fornon-invasively measuring uterine activity, in particular contractionsduring labor, without the need for expensive equipment replacement wouldbe beneficial. Also, a cost-effective sensor and/or monitoring systemfor both the mother and fetus that can continuously monitor, inreal-time, and accurately extract and evaluate maternal/fetal heartrates and ECGs, and maternal EHG, without the need for expensiveequipment replacement, would be beneficial.

BRIEF SUMMARY OF THE INVENTION

Without limitation, the term sensor refers to either an acoustic sensorsuch as a microphone, an electric sensor such as an electrode, or anynumber of other types of sensors useful in extracting maternal-fetalinformation. The present invention provides a unique interface systemthat converts sensor signals containing information of the maternal andfetal heart rate and ECG, and maternal muscle activity captured bynon-standard sensors (such as for ECG electrodes and acoustic sensors)into signals that provide inputs of uterine activity and heart rate andECG to a maternal-fetal monitor without the use of existing sensors. Asused herein, the term “existing sensor” refers to an intra-uterinepressure catheter (IUPC) sensor, a tocodynamometer sensor, a fetal scalpelectrode sensor, or an ultrasound sensor. For example, existing sensorsare generally the sensors that are typically used with thematernal-fetal monitor and/or the sensors provided or sold with thematernal-fetal monitor. As used herein, the term “non-standard sensor”refers to a sensor that is not an IUPC sensor, a tocodynamometer sensor,a fetal scalp electrode sensor, or an ultrasound sensor. These“standard” sensors are typically used with maternal-fetal monitors, but,in an embodiment, the subject invention can convert sensor signalscaptured by non-standard sensors into signals that provide inputs ofuterine activity and heart rate and ECG to a maternal-fetal monitorwithout the use of existing sensors.

The present invention provides a unique interface system that convertselectrical muscle activity captured by common electrodes (such as forECG/EMG) into signals that provide uterine activity data to amaternal-fetal monitor without the use of a tocodynamometer.

Preferably, the interface system comprises a cable that converts outputfrom electrodes or sensors to an output comparable to those provided bya tocodynamometer, IUP, FSE, or ultrasound monitor (collectively PROBE)for connection to a maternal-fetal monitor. The monitor can beconfigured for a uterine activity sensor (such as a tocodynamometer, anintrauterine pressure catheter, a fetal scalp electrode, and the like).

In one embodiment, the interface system of the invention comprises aninterface (also referred to herein as a connector) for at least oneelectrode, an interface for a compatible port in a maternal-fetalmonitor, and a signal converter for converting electrode output providedthrough the electrode interface to output comparable to those providedby a tocodynamometer.

In one embodiment, the interface system of the invention comprises aninterface (also referred to herein as a connector) for at least onesensor, an interface for a compatible port in a maternal-fetal monitor,and a signal converter for converting sensor output provided through thesensor interface to output comparable to those provided by a standardPROBE.

In one embodiment, the interface system comprises a cable portion formedintegrally with an electrode interface, a maternal-fetal monitor portinterface, and a signal converter to provide a unitary cable structure.In another embodiment, the interface system comprises an electrodeinterface that includes a wireless signal transmitter, a maternal-fetalmonitor port interface, and a signal converter that includes a wirelesssignal receiver, wherein all of these components are physicallyindependent from each other.

In one embodiment, the interface system comprises a cable portion formedintegrally with a sensor interface, a maternal-fetal monitor portinterface, and a signal converter to provide a unitary cable structure.In another embodiment, the interface system comprises a sensor interfacethat includes a wireless signal transmitter, a maternal-fetal monitorport interface, and a signal converter that includes a wireless signalreceiver, wherein all of these components are physically independentfrom each other or combined in different combinations.

In an embodiment, the interface system comprises an electrode interfacefor multiple electrodes, more preferably between 2 and 6 electrodes.Preferably, the maternal-fetal monitor port interface is operablyconnectable with a uterine activity port or a tocodynamometer portavailable on the maternal-fetal monitor.

In a preferred embodiment, the interface system comprises a sensorinterface for multiple sensors, more preferably between 2 and 8 sensors.Preferably, the maternal-fetal monitor port interface is operablyconnectable with one or more ports on the maternal-fetal monitor.

In an embodiment, an interface system can include: a sensor interfacefor operably connecting to at least one maternal abdominal sensor andreceiving at least one signal from the at least one maternal abdominalsensor; a signal converter connected to the sensor interface, whereinthe signal converter processes the at least one signal into output datathat mimics electrical output from a tocodynamometer, intra-uterinepressure catheter, fetal scalp electrode, and/or ultrasound device; anda maternal-fetal monitor port interface for operably and physicallyconnecting to a maternal-fetal monitor, wherein the maternal abdominalsensor is not a tocodynamometer or an ultrasound sensor.

In an embodiment, a sensor array designed for a maternal abdomen caninclude: a substrate; at least two sensors on the substrate; and acurved electrical connection connected to each sensor, wherein eachcurved electrical connection is configured to allow the sensor array toconform to the shape of the maternal abdomen.

In an embodiment, a method of optically coupling a signal converter anda maternal-fetal port, wherein the signal converter comprises an LEDcircuit, can include: providing an optical interface for thematernal-fetal port, wherein the optical interface comprises anoptically-isolated balanced bridge circuit comprising a photo-resistoroptically coupled to the LED circuit; driving the LED circuit with avoltage-to-current converter device, thereby modulating a currentthrough the LED circuit and creating a maternal-fetal port input signal;and providing the maternal-fetal port input signal to the maternal-fetalport.

The present invention provides a new and improved interface system thathas the ability to provide accurate contraction and cardiac data byconverting electrode or sensor signals into PROBE-comparable data thatcan be processed using commercially available maternal-fetal monitors.The present invention is particularly advantageous because of low costsof manufacture with regard to both materials and labor, whichaccordingly induces low prices of sales to the consuming public.

Other features and advantages of the invention will be apparent from thefollowing description and accompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 illustrates one embodiment of the invention wherein an interfacecable of the invention is operatively connected to a strip of electrodesor sensors and a maternal-fetal monitor.

FIG. 2 illustrates a power adapter that can be used in combination withthe interface cable of the invention.

FIG. 3 illustrates a strip of electrodes or sensors that can be used incombination with the interface cable of the invention.

FIG. 4 is a flow diagram illustrating the process for convertingelectrode or sensor input to tocodynamometer-like data within theinterface cable.

FIG. 5 illustrates another embodiment of the invention comprising awireless interface connection between an electrode strip or sensor stripand maternal-fetal monitor.

FIG. 6 illustrates one process for producing an electrical analogequivalent to a tocodynamometer signal from electrode or sensor signals.

FIG. 7 illustrates a uterine activity connector pinout in amaternal-fetal monitor.

FIGS. 8A-8C illustrate a square-type cable for interfacing a fetal scalpelectrode with a maternal-fetal monitor, including the cable pinoutdiagram and a “square-type” connector pinout for the fetal scalpelectrode cable in a maternal-fetal monitor.

FIGS. 9A-9C illustrate another cable for interfacing a fetal scalpelectrode with a maternal-fetal monitor, including the cable pinoutdiagram and a “circular-type” connector pinout for the fetal scalpelectrode cable in a maternal-fetal monitor.

FIGS. 10A-10C illustrate a cable for interfacing an intra-uterinepressure catheter (IUPC) with a maternal-fetal monitor, including thecable pinout diagram and a “circular-type” connector pinout for the IUPCcable in a maternal-fetal monitor.

FIGS. 11A-11C illustrate yet another cable for interfacing a fetal scalpelectrode with a maternal-fetal monitor, including the cable pinoutdiagram and the corresponding connector pinout for the fetal scalpelectrode cable in a maternal-fetal monitor.

FIGS. 12A-12C illustrate another cable for interfacing an intra-uterinepressure catheter (IUPC) with a maternal-fetal monitor, including thecable pinout diagram and the corresponding connector pinout for the IUPCcable in a maternal-fetal monitor.

FIG. 13 illustrates identifying connection information for the cablepinout and corresponding connector pinout of FIGS. 12B and 12C.

FIG. 14 illustrates the differences in accuracy for contraction patternsmonitored in obese women with a tocodynamometer versus EHG-derivedcontraction patterns.

FIG. 15 illustrates a maternal-fetal monitor including a connectorpinout suitable for use with the interface cable of the invention.

FIG. 16 illustrates heart sounds in relation to hemodynamic events andECGs.

FIG. 17 illustrates an enveloped signal.

FIG. 18 illustrates a functional block diagram of a sensor interfacesystem according to an embodiment of the subject invention. An electrodeand acoustic sensor array (left) can interface to a cable containing asignal converter (middle) and a fetal monitor interface (right).

FIG. 19 illustrates a functional block diagram of a novel design,according to an embodiment of the subject invention, to interface to atoco port of an existing maternal-fetal monitor.

FIG. 20 illustrates a functional block diagram of a novel design,according to an embodiment of the subject invention, to interface to anFECG port of an existing maternal-fetal monitor.

FIG. 21 illustrates a diagram of a sensor array, according to anembodiment of the subject invention, with features specifically designedfor maternal abdomens.

FIG. 22 illustrates a sensor array template, according to an embodimentof the subject invention, for utilizing off the shelf sensors.

FIG. 23 illustrates one embodiment of the invention wherein an interfacecable of the invention is operatively connected to a strip of electrodesor sensors and a maternal-fetal monitor.

FIG. 24 illustrates a power adapter that can be used in combination withthe interface cable of the invention.

FIG. 25 illustrates a strip of electrodes or sensors that can be used incombination with the interface cable of the invention.

FIG. 26 illustrates another embodiment of the invention comprising awireless interface connection between an electrode strip or sensor stripand maternal-fetal monitor.

DETAILED DISCLOSURE

The present invention provides a unique interface system that convertselectrical muscle activity signals captured by at least one electrodeinto signals that provide uterine activity data to a conventionalmaternal-fetal monitor without the use of a tocodynamometer or invasivematernal-fetal monitoring device (such as an intra-uterine pressurecatheter (IUPC) or fetal scalp electrode). The information provided bythe interface system can then be processed by the maternal-fetal monitorto generate information regarding EHG signals, uterine contractionduring and after labor, uterine atony, intrauterine pressure, Montevideounits, and the like.

In one embodiment, as illustrated in FIGS. 1 and 23, the interfacesystem comprises a cable integrally formed with an electrode interface10 (or also referred to herein as a connector), a maternal-fetal monitorport interface 20, and a signal converter 15 that converts outputsignals from electrodes to an output signal comparable to those providedby a tocodynamometer or IUPC. The interface system is preferably in theform of a unitary cable structure. The electrode interface 10 can beconnected to any conventional electrode or set of electrodes 5.

The present invention provides a unique interface system that convertssignals captured by at least one sensor into signals that provide PROBEdata to a conventional maternal-fetal monitor without the use of astandard PROBES (such as an intra-uterine pressure catheter (IUPC),ultrasound (U/S), tocodynamometer (toco) or fetal scalp electrode(FSE)). The information provided by the interface system can then beprocessed by the maternal-fetal monitor to generate informationregarding uterine contraction during and after labor, uterine atony,intrauterine pressure, Montevideo units, fetal heart rate,decelerations, fetal ECG, fetal distress, and the like.

In an embodiment, as illustrated in FIGS. 1 and 23, the interface systemcomprises a cable integrally formed with a sensor interface 10 (or alsoreferred to herein as a connector), a maternal-fetal monitor portinterface 20, and a signal converter 15 that converts output signalsfrom sensors to an output signal comparable to those provided by aPROBE. The interface system is preferably in the form of a unitary cablestructure. The sensor interface 10 can be connected to any conventionalsensor or set of sensors 5.

The cable can transmit analog, digital, or a combination of analog anddigital signals. In certain embodiments, the cable is specificallydesigned for communication/connection with a conventional maternal-fetalmonitor 25. For example, a cable can be preprogrammed with the expectedvoltage range for the monitor.

In a related embodiment, the cable uses the same power as that suppliedby the maternal-fetal monitor, and thus will not require a separatepower supply. In certain embodiments, as illustrated in FIGS. 2 and 24,an additional power connector is included in the system that allows forpermanent power connectivity. The power connector can be designed as asemi-permanent adapter 30 connected to the maternal-fetal monitor thatallows both standard tocodynamometer (or IUPC) cables 35 and an EHGcable 40 to be plugged into it without removing the adapter from themonitor 25. In this way, the power system can be attached to the monitoronce and not removed, allowing repeated swapping of the tocodynamometer(or IUPC) cable and the interface system of the present inventionwithout undue hassle.

The electrode interface can be connected to any conventional electrodeor set of electrodes including, but not limited to, disposableelectrodes (including electrodes that are without gel and pregelled),reusable disc electrodes (including gold, silver, stainless steel, ortin electrodes), headbands, and saline-based electrodes. Contemplatedelectrodes include those used for monitoring electrocardiography(ECG/EKG); electroencephalography (EEG); electromyography (EMG);electonystagmography (ENG); electro-oculography (EOG), printed circuitelectrodes, and electroretinography (ERG).

In a preferred embodiment, as illustrated in FIGS. 3 and 25, theinterface system comprises an electrode interface for a plurality ofelectrodes, more preferably between 2 and 6 electrodes. Preferably, theelectrodes are provided on a strip or mesh 5, including a singleconnector 10 for the electrode interface of the invention. Theelectrodes can be bipolor or monopolar in nature. The electrodes arepreferably AgAgCl sensors with a surface area of 27 mm² wet gel. Incertain related embodiments, there is an adhesive area surrounding thesensor area. The electrodes can be placed in a wide variety of locationson the patient, including over the uterus.

In a related embodiment, the cable uses the same power as that suppliedby the maternal-fetal monitor, and thus will not require a separatepower supply. In certain embodiments, as illustrated in FIGS. 2 and 24,an additional power connector is included in the system that allows forpermanent power connectivity. The power connector can be designed as asemi-permanent adapter 30 connected to the maternal-fetal monitor thatallows both PROBE cables 35 and an sensor cables 40 to be plugged intoit without removing the adapter from the monitor 25. In this way, thepower system can be attached to the monitor once and not removed,allowing repeated swapping of the PROBE cable and the interface systemof the present invention without undue hassle.

The sensor interface can be connected to any conventional sensor or setof sensors including, but not limited to, disposable sensors (includingsensors that are without gel or pregelled), reusable disc electrodes(including gold, silver, stainless steel, or tin electrodes), headbands,saline-based electrodes, impedance, radio frequency (RF), and acousticsensors. Contemplated sensors include those used for monitoringelectrocardiography (ECG/EKG); electroencephalography (EEG);electromyography (EMG); electonystagmography (ENG); electro-oculography(EOG), printed circuit sensors, electroretinography (ERG), bioimpedancesensors (RF or otherwise) and stethoscope sensors.

In a preferred embodiment, as illustrated in FIGS. 3 and 25, theinterface system comprises a sensor interface for a plurality ofsensors, more preferably between 2 and 8 sensors. FIG. 18 illustrates afunctional block diagram of a sensor interface system according to anembodiment of the subject invention. An electrode and acoustic sensorarray (left) can interface to a cable containing a signal converter(middle) and a fetal monitor interface (right). Referring to FIG. 18,preferably, the sensors are provided on a strip or mesh 5, including asingle connector 10 for the sensor interface of the invention. Electrodesensors can be bipolar or monopolar in nature. The electrode sensors arepreferably AgAgCl sensors with a surface area of 27 mm² wet gel. Incertain related embodiments, there is an adhesive area surrounding thesensor area. The sensors can be placed in a wide variety of locations onthe patient, including over the uterus.

In a preferred embodiment, the signal converter of the inventionincludes a microprocessor, digital signal processor, or otherprogrammable device that converts electrode or sensor signal data intoan electrical analog of a Wheatstone bridge configuration that isnormally used in a tocodynamometer. An illustration of a Wheatstonebridge configuration used in a conventional tocodynamometer isillustrated in FIG. 6. A tocodynamometer generally transforms strain tothe strain gauge/sensor into a proportional change of resistance. Giventhe linear Wheatstone bridge configuration, differential output voltagesare produced that are linearly related to the strain applied to thegauge/sensor. These differential output voltages are produced at the (+)and (−) pressure ports at mV amplitude levels. In certain instances,these small differential output voltages are subsequently amplified inthe fetal/maternal monitor using a differential-input instrumentationamplifier configuration.

According to one embodiment of the subject invention, as illustrated inFIG. 4, the signal converter 15 includes a programmable device 55 and ananalog to digital converter 50 that converts EHG or sensor signalsderived from the electrode or sensor interface from analog signals to adigital output, where the digital output is then processed by theprogrammable device. The programmable device determines the appropriatevoltage level required to mimic the output of the PROBE based upon thedigital output signals received. This voltage level can then beconverted back to an analog signal using a digital to analog converter60, pulse width modulation circuit, or other method.

In another embodiment, the signal converter includes a microprocessor 55that calculates the desired uterine activity from the EHG or sensorsignals. The microprocessor interfaces to the monitor via amicroprocessor-controlled digital potentiometer, where the potentiometersimulates the strain gauge resistances seen at the legs of theWheatstone bridge. This solution would mimic the tocodynamometer itself,instead of just the voltages output from the tocodynamometer. Thedesired signal would be driven on the Wheatstone bridge in a mattersimilar to the tocodynamometer itself, thus creating an EHG emulation ofa tocodynamometer that is more compatible with different types of fetalmonitors.

In a preferred embodiment, the fetal monitoring ports are driven with anoptical coupling method that provides simple and effective completeelectrical isolation between the system and the fetal monitor. FIG. 19shows an interface, according to an embodiment of the subject invention,to a fetal monitor connection, e.g. a toco connection. The opticalinterface for the fetal monitor toco input creates an optically-isolatedbalanced bridge circuit that is essentially identical to a standardtocodynamometer bridge circuit, but uses a photo-resistor instead of aresistive strain gauge in one leg of the bridge. The photo-resistor isoptically coupled to an LED circuit driven by a pulse-width modulated(PWM) digital-to-analog converter (ADC) and voltage-to-current converteramplifier device. The analog contraction curve signal from the ADCcircuit modulates the current through the LED, and through the opticalcoupling to the bridge photo-resistor, creates a toco signal at thebridge outputs that is fed to the fetal monitor toco input connector.

FIG. 20 illustrates an optical interface, according to an embodiment ofthe subject invention, for the fetal monitor Fetal ECG input. It createsa millivolt-level pulse signal that simulates a fetal heartbeat ECGsignal. A simulated fetal heartbeat pulse is generated by the signalconverter, and it is output through the analog-to-digital converter(ADC) circuit that drives the input of a current-to-voltage amplifiercircuit. The current-to-voltage amplifier drives an output currentthrough an infrared LED that generates an optical fetal heartbeat pulsesignal. This optical fetal heartbeat signal is optically coupled to aphotodiode, which converts the optical signal into an electrical signalthat is fed to the fetal monitor FECG input connector.

In certain embodiments, the microprocessor includes a means forfiltering 45 of the signals generated from the electrodes or sensors. Inone embodiment, the microprocessor includes: (1) a high pass filter atvery low frequency (0.005 Hz) to remove the DC offset and noise, and (2)a low pass filtered with another low frequency filter (0.025 Hz). In arelated embodiment, the microprocessor includes a high pass filter at avery low frequency and a standard power estimation method such as RMS orother squaring methods. More complex signal processing methods such aswavelets, blind source separation, nonlinear filtering, and frequencyanalysis can also be utilized.

Multiple signal channels can be included at the electrode or sensorinterface to reduce noise characteristics. The multiple channels can beprocessed by the signal converter in many ways. For example, the signalscan simply be added to each other or subtracted from each other for morerobustness to noise. Additionally, attributes can be calculated on eachsignal and those signals with the best characteristics (e.g. signal tonoise ratio) can be used to create the uterine activity signal.

In an alternative embodiment, the microprocessor and digital portion ofthe system would be replaced with a completely analog system. Analogfilters can be created with resistors, capacitors, and amplifiers can beembedded into the signal converter to convert the EHG or sensor signalsto PROBE-like signals. Analog circuitry can be designed using discretecomponents or integrated components such as ASICs (application specificintegrated circuits). Since the conversion from EHG or sensor electricalinterface to PROBE electrical interface is externally, simply a voltageconversion, analog filtering can be created to modify the EHG or sensorsignals and create signals that mimic those expected by the fetalmonitor.

In yet another embodiment, the signal converter includes both analog anddigital processing. The analog processing would typically include pre-or post-processing of the signals. For example anti-aliasing filters orother filtering techniques can be implemented by the signal converter.Similarly, the signal converter could apply signal conditioning to theoutput signal to appropriately mimic the signal output from a PROBE.

FIG. 21 illustrates a multi-sensor interface, according to an embodimentof the subject invention, to the signal converter that is speciallydesigned to interface to a pregnant subject's abdomen. The multi-sensorinterface, herein called a mesh, is made of a substrate that containselectrical material between the connector and the sensors. Theelectrical material can be, for example, printed, painted, or sewnbetween the connector and the sensors. The curved lines in the mesh aredesigned to wrap around the curved surface of the maternal abdomen. Theserpentine shape (B) on each arm allows the mesh to flex and stretcharound different shaped abdomens and as the subject moves. Theserpentine shape can be rounded or linear. Each serpentine shape caninclude two or more curves or changes of direction of 180 degrees orabout 180 degrees. For example, each serpentine shape can include two,three, four, five, six, or more curves or changes of direction (of 180degrees or about 180 degrees). The alignment piece (A) of the mesh,called the electrode directional alignment template (EDAT), allows forproper alignment of the mesh as well as greatly simplifying theplacement of the sensor mesh. The EDAT is connected to some or all ofthe electrodes. The EDAT is preferably connected to some or all of theelectrodes with a perforated form or tabbed release liner. The meshcomes formed with an adhesive backing and a release liner. When placed,the nurse can remove the release liner and place the sensor mesh withalignment center piece (EDAT) on the abdomen. Once placed, the alignmentpiece can be removed to allow the mesh to move freely and comfortably onthe maternal abdomen while maintaining good connectivity.

FIG. 22 illustrates a template, according to an embodiment of thesubject invention, that allows individual sensors to be connected to thesystem with accurate placement and cable management. The template 105can be made of, for example, fabric or plastic. The template 105 hasmechanisms to hold the sensors in place at different locations on theabdomen 100 while including mechanisms to hold the wires between thesensors and connector in place. The wires can be, for example, painted,printed, or sewn onto/into the substrate.

In another embodiment, acoustic sensors are included. The heart'speriodic activity is controlled by an electrical conducting system. Thissystem initiates the electrical signal in specialized pacemaker cellsthat are then propagated through the atria to the AV-node and to theventricles. In turn, this electrical action potential (used in ECGanalysis) excites the muscle cells and causes the mechanical contractionof the heart chambers from which four audible heart sounds aregenerated. The sequence of events that generates the heart sounds isoften referred to as the cardiac cycle.

FIG. 16 illustrates how the four heart sounds are correlated to theelectrical and mechanical events of the cardiac cycle. The first heartsound (S1) occurs during the systole phase of the cardiac cycle. It ischaracterized by a higher amplitude and longer duration in comparisonwith other heart sounds. The duration of S1 lasts for an average periodof 100-200 ms. It also has two major high-frequency components in therange of 10-200 Hz that can be easily distinguished. These twocomponents are often separated by a time delay of 20-30 ms and coincidewith the RS interval of the electrocardiogram (ECG). Overall, theacoustic properties of S1 are able to reveal the strength of themyocardial systole and the status of the atrioventricular valves'function.

The second heart sound (S2) occurs during the diastole phase andcoincides with the completion of the T-wave of the ECG. The producedsound usually has higher-frequency components (as high as 400 Hz) ascompared with the first heart sound. Since the aortic valve tends toclose before the pulmonary valve, the interval between the componentscan often vary. Further variations of the time interval can be caused byrespiration. For example, during expiration phase, the interval betweenthe two components is small (less than 30 ms). However, duringinspiration, the interval between the two components is much larger.

The third (S3) and fourth heart sounds (S4), also called gallop sounds,are low-frequency sounds (15-60 Hz) occurring in early and late diastole(within 120 ms P-wave of the ECG), respectively. Although a normal S3 isaudible in children and adolescents it is not audible in most adults.Alternatively, the fourth heart sound is seldom audible in normalindividuals without the use of highly sensitive sensors.

Overall, the different heart sounds give us various pieces ofinformation about the cardiac activity. Integrating this informationwith the information provided by the electrical conducting system(through the use of ECG) should yield better signal processingtechniques or improvements on existing methods.

Using the acoustic information allows easier acquisition of the FetalHeart Rate (FHR). Under normal conditions, the Fetal Electrocardiogram(FECG) is susceptible to noise interference of the mother's electricalsignal and/or muscle contractions. Using the acoustic information of themother and child help refine the independent signals and provide formore robust separations since the acoustic information would not beeffected by the mother's contractions. Additionally, S3 and S4 are onlyobservable in the healthy hearts of children. This may allow for anotherway to separate the maternal heart rate from the fetus.

One algorithm for acquiring the FHR involves detecting the maternalheart rate (MHR) in the ECG signal. This would include channel averagingor subtraction across the four ECG channels to remove noise. Then adetection of the periodic signal with the most energy should correspondto the heart rate of the mother. Once the MHR signal is acquired, amatched filter could be formed from a portion of the QRS MHR signal andsummarily subtracted from the filtered version of the MHR. This processshould leave most of the FHR on the ECG signal and attenuate the MHR.Finally, a low-passed average energy measure would be applied to theremaining signal in order to generate a signal envelope (FIG. 17). Thiswould complete phase one.

Phase two would require a similar process on the phonocardiogram.Although there may be a dependence on the location of the acousticsensors, the channels can first be averaged or subtracted to eliminatenoise. Then homomorphic filtering would be applied to the cleanedphonocardiogram along with a low passed-average energy measure in orderto generate a signal envelope. As above, the periodic signal can bedetected with the largest energy to determine the maternal heart signal.The matched filtered version of the enveloped signal can then besubtracted from the enveloped signal. This would leave S2 and the fetalphonocardiogram signals. Another pass of the above described algorithmwould be used to remove S2 and leave the fetal acoustic signal.

For the final phase of the algorithm, the FHR signal envelope acquiredfrom the ECG would be cross correlated with the FHR signal envelopeacquired from phonocardiogram at different lags (under 200 ms). Thecorrelation peaks would relate to a true FHR signal (using some sort ofpeak detector).

A wireless embodiment is contemplated herein, see FIGS. 5 and 26. Theinterface system comprises an electrode or sensor interface 10, awireless signal transmitter 65, a wireless signal receiver 70, a signalconverter 15, and a maternal-fetal monitor port interface 20. Accordingto the subject invention, these components can be physically independentfrom each other or presented in various combinations to form a singlecomponent. For example, the electrode or sensor interface and wirelesssignal transmitter can be presented together as a single component; thewireless signal receiver and signal converter can be presented togetheras a single component; the signal converter and wireless signaltransmitter can be presented together as a single component; thematernal-fetal port interface, the signal converter, and the wirelesssignal receiver can be presented together as a single component.

According to one embodiment, a wireless signal transmitter is operablyconnected to an electrode or sensor interface, which is connected to theelectrode(s) or sensor(s). The wireless signal transmitter can include adata storage device (such as a magnetic hard drive, flash memory card,and the like). Preferably, the wireless signal transmitter includescommunications protocols for data representation, signaling,authentication, and error detection that is required to send informationover a wireless communications channel (i.e., a specific radio frequencyor band of frequencies such as Wi-Fi, which consists of unlicensedchannels 1-13 from 2412 MHz to 2484 MHz in 5 MHz steps). The wirelesssignal transmitter is preferably located in close proximity to thepatient or on the patient's body. For example, the wireless signaltransmitter can be attached to the side of the bed or the patient's arm.In certain embodiments, the signal converter is operably connected tothe wireless signal transmitter or presented together with the wirelesssignal transmitter as a single component.

A wireless signal receiver is also included in the wireless embodiment.The wireless signal receiver is operably connected to a signal converterand/or maternal-fetal monitor port interface. The wireless signalreceiver is preferably configured with communications protocols toreceive information over a wireless communications channel.

Many wireless transmission communications protocols exist and areapplicable to the wireless signal transmitter/receiver of thisinvention, including Bluetooth, Wi-Fi, Zigbie, wireless USB, etc. Thewireless transmission of information from the wireless signaltransmitter to the wireless signal receiver could be in digital formator in analog format.

In certain embodiments, the wireless signal transmitter (and/or wirelesssignal receiver) includes an internal power source (i.e., batteries, andthe like). Alternatively, the wireless signal transmitter (and/orwireless signal receiver) does not require an internal power source.This can be accomplished with a variety of energy harvesting or wirelesspower transmission methods such as harvesting of heat, movement,electrical signals from the environment, or inductive coupling. In oneembodiment, this is accomplished by using an antenna to convert radiatedor inducted power into usable energy for the transmission of the desiredsignals. For example, the wireless signal transmitter can be an antennathat is commonly used in radio frequency identification tags (or RFIDtags), where minute electrical current induced in the antenna by anincoming radio frequency signal provides just enough power for anintegrated circuit (IC) in the RFID tag to power up and transmit aresponse (for example, to a wireless signal receiver of the invention).

In another embodiment, the EHG or sensor signal is digitized and storedin memory either in the electrode or sensor interface, the signalconverter, or the maternal-fetal monitor port interface. The stored datacan be transmitted periodically or at a later time. This delayedtransmission may, without restriction, be utilized to improve batterylife by transmitting data transiently, instead of continuously; or toallow for patient monitoring during disconnection from the monitor.

In operation, the electrode or sensor interface accepts EHG or sensorsignals from the electrode(s) or sensor(s) and transmits the signals tothe maternal-fetal port interface via the wireless signal transmitterand wireless signal receiver. The signal converter can be operablyconnected to either the wireless signal transmitter or the wirelesssignal receiver, where the signal converter processes the electrode orsensor signals and/or performs digital/analog signal conversions.

In one embodiment, the electrode interface attached to the electrodescontains a signal converter that can perform analog to digitalconversion and process EHG signals into an equivalent tocodynamometer orIUPC voltage. The wireless signal transmitter would then digitallytransmit this data to the wireless signal receiver, which wouldcommunicate the data through the maternal-fetal port interface to thematernal-fetal monitor. Preferably, the data provided to thematernal-fetal monitor mimics data format normally provided by atocodynamometer or IUPC.

In one embodiment, the sensor interface attached to the sensors containsa signal converter that can perform analog to digital conversion andprocess signals into an equivalent PROBE. The wireless signaltransmitter would then digitally transmit this data to the wirelesssignal receiver, which would communicate the data through thematernal-fetal port interface to the maternal-fetal monitor. Preferably,the data provided to the maternal-fetal monitor mimics data formatnormally provided by a PROBE.

In another embodiment, the electrode interface includes a means forconverting analog signals to digital signals, and the resultant digitalsignals are transmitted via the wireless signal transmitter to thewireless signal receiver. The wireless signal receiver is operablyconnected to a signal converter that processes the digital signals intoa format equivalent to tocodynamometer or IUPC data, which issubsequently communicated to the maternal-fetal monitor via thematernal-fetal monitor port interface.

In another embodiment, the sensor interface includes a means forconverting analog signals to digital signals, and the resultant digitalsignals are transmitted via the wireless signal transmitter to thewireless signal receiver. The wireless signal receiver is operablyconnected to a signal converter that processes the digital signals intoa format equivalent to PROBE data, which is subsequently communicated tothe maternal-fetal monitor via the maternal-fetal monitor portinterface.

In yet another embodiment, the raw analog signals generated by theelectrodes are communicated via the electrode interface and wirelesssignal transmitter to a wireless signal receiver. The wireless signalreceiver is operably connected to a signal converter that converts theraw analog signals to digital signals, which are subsequently processedby the signal converter into a format equivalent to tocodynamometer orIUPC data. The tocodynamometer or IUPC data is subsequently communicatedto the maternal-fetal monitor via the maternal-fetal monitor portinterface.

In yet another embodiment, the raw analog signals generated by thesensors are communicated via the sensor interface and wireless signaltransmitter to a wireless signal receiver. The wireless signal receiveris operably connected to a signal converter that converts the raw analogsignals to digital signals, which are subsequently processed by thesignal converter into a format equivalent to PROBE data. The PROBE datais subsequently communicated to the maternal-fetal monitor via thematernal-fetal monitor port interface.

According to the present invention, the electrode or sensor interfacecan also be operably connected to a fetal heart rate sensor (such as anultrasound, fetal scalp electrode, or fetal scalp sensor) with orwithout a uterine activity sensor. Data collected from the fetal heartrate sensor can be communicated to a maternal-fetal monitor via thecable embodiment or the wireless embodiment described above.

As illustrated in FIG. 15, the maternal-fetal monitor port interface ofthe invention can be operatively connected to a maternal-fetal monitorport 80 (also referred to herein as a pinout) configured for aconventional uterine activity sensor (such as a tocodynamometer, anintrauterine pressure catheter, a fetal scalp electrode, fetal scalpsensor, and the like). Preferably, the maternal-fetal monitor portinterface is operably connectable with a uterine activity port or atocodynamometer port available on a conventional maternal-fetal monitor25. Similarly, the system interfaces to a FECG or U/S port to providefetal cardiac data.

Maternal-fetal monitor port interface preferably consists of appropriateconnectors to maternal-fetal monitors from different manufacturershaving different pinout/port configurations (see FIGS. 7-13). One suchexample of interfacing to both COROMETRICS® and AGILENT® is provided bythe METRON® PS-320 patient simulator. This simulator uses a number ofcustom cables for interface to these monitors. Pinout/port informationfor commonly available maternal-fetal monitors are provided in Table 1:

TABLE 1 Uterine Activity Connector Pinout for Corometrics 116 MonitorPin # Signal Name Signal Description 1 (+) Pressure Positive Input toPressure Amp 2 (−) Pressure Negative Input to Pressure Amp 3 NC NoConnection 4 +4 Volt Excitation +4 Volt Reference to Bridge 5 NC NoConnection 6 GND (Excitation Ref) +4 Volt Reference Ground 7 UA ShieldShield 8 NC No Connection 9 NC No Connection 10 NC No Connection 11 IUPEnable IUP ENABLE (ACTIVE LOW) 12 TOCO Enable TOCO ENABLE (ACTIVE LOW)

EXAMPLE 1

As noted above, labor contractions are typically monitored with a straingauge (such as a tocodynamometer), which provides frequency andapproximate duration of labor contractions. Unfortunately, in obesepatients, the distance from the skin to the uterus may be such that thetocodynamometer does not detect contractions reliably. In this setting,or when quantitative measurement of intrauterine pressure (IUP) isdeemed necessary, an invasive IUP catheter (IUP) is commonly required.The electrical activity of the uterus, or electrohysterogram (EHG) asmonitored using sensors, has long been recognized as linked tomechanical activity. This Example provides a study that compared theaccuracy of EHG-derived contractions with those provided by atocodynamometer and IUP monitoring in clinically severely obese laboringwomen.

Participants

This Example evaluated data from 14 laboring subjects with body massindex (BMI)≧34 who had an IUPC placed during EHG monitoring. 30 minutesegments were selected before and after placement.

Methods

An array of eight 3-cm²Ag/AgCl₂ electrodes was placed over maternalabdomen and signals amplified with high gain, low noise amplifiers. Allsignals were measured with respect to a reference electrode, with drivenright leg circuitry to reduce common mode noise. The amplifier 3 dBbandwidth was 0.1 Hz to 100 Hz, with a 60 Hz notch. The contractionlocation was derived by down-sampling the signal at 20 Hz. Contractionswere rejected if duration was less than 30 seconds or greater than 120seconds, with an amplitude less than 30% of the median of the last 10contractions (a minimum amplitude of 5 units was also applied for eachtocodynamometer/IUPC). The contraction correlation index (CCI)⁽¹⁾=#consistent contractions/½(# tocodynamometer/IUPC-derived contractions+#EHG-derived contractions) was evaluated. In addition, the frequency ofunreliable uterine activity monitoring, using IUP as the standard forcomparison, was also evaluated.

Results

Of the 14 patients (BMI 45.1±7.9), 6 underwent amniotomy at the time ofIUPC placement. During the first half of the study, the tocodynamometeridentified 155 contractions while the EHG identified 195 contractions.After placement of the IUP, the IUP identified 192 contractions, versus185 EHG-derived contractions. The CCI between EHG and thetocodynamometer was 0.79±0.29 and the CCI was 0.92±12 between EHG andIUP (p=0.07, ns). These results demonstrate that the tocodynamometer maybe unreliable in clinically severely obese patients. As illustrated inFIG. 14, the EHG-derived contraction pattern in the obese women in thisstudy correlated better with IUP than the tocodynamometer, exceeding 90%correlation in 13/14 patients versus 10/14 for the tocodynamometer.

All patents, patent applications, provisional applications, andpublications referred to or cited herein are incorporated by referencein their entirety, including all figures and tables, to the extent theyare not inconsistent with the explicit teachings of this specification.

It should be understood that the examples and embodiments describedherein are for illustrative purposes only and that various modificationsor changes in light thereof will be suggested to persons skilled in theart and are to be included within the spirit and purview of thisapplication.

We claim:
 1. An interface system comprising: a sensor interface for operably connecting to at least one maternal abdominal sensor and receiving at least one signal from the at least one maternal abdominal sensor; a signal converter connected to the sensor interface, wherein the signal converter processes the at least one signal into output data that mimics electrical output from a tocodynamometer, intra-uterine pressure catheter, fetal scalp electrode, and/or ultrasound device; and a maternal-fetal monitor port interface for operably and physically connecting to a maternal-fetal monitor, wherein the maternal abdominal sensor is not a tocodynamometer or an ultrasound sensor. 